Wtred-radio broadcasting system



Filed may. 1927 F @emencs R. D. DUNCAN, JR

VIIRED RADIO BROADCASTING SYSTEM Mrealhdz'a-mmtdn9 May 8, 1928,

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UNITED STATES PATENT OFFICE.

ROBERT D. DUNCAN, JR., 0F EAST ORANGE, NEW JERSEY, .ASSIGNOR T0 WIREDRADIO, INC., 0F NEW YORK, N. Y., A CORPORATION 0F DELAWARE.

WIRED-RADIO BROADCASTING SYSTEM.

Application filed May 7, 1927. Serial No. 189,691.

My invention relates broadly to the broadcasting of high frequencysignaling currents over line wire systems and more particularly to abroadcastin system employing power lines as a guide or the highfrequency currents.

One of the objects of my invention is to provide a method of alteringthe natural frequency of distribution transformers in a power linesystem foi` facilitating the transmission of high frequency currents towired radio receivers in the homes of lighting customers.

Another object of my invention is to provide means for obtaining uniformattenuation of the high frequency energy over a power line distributionsystem by correcting in a graduated manner the different distributiontransformers between the power generation station and the receivers oflighting customers for the eicient operation of wired radio receivers atvarious points in the system.

M invention will be more fully understoo from the followingspecification by reference to the accompanying drawings, wherein:

Figure 1 shows diagrammatically a power line distribution systemindicating the arrangement therein of power transformers, the lightingload and the wired radio receiver for installation in the home of alighting customer; Fig. 2 shows a set of typical characteristic curvesfor a number of power transformers in a wired radio broadcasting system;Fig. 3 shows diagrammatically the improved clrcuit arrangements of myinvention; and Fig. 4 illustrates the characteristic curves obtainablein the improved system of my invention.

In a wired radio broadcasting system wherein high frequency currents aresuperimposed upon an electric power distribution system or transmissionline, the high frequency power is usually introduced into the system ata point adjacent the power substation, from which point the current Howsover the primary feeders, through the distribution transformers and overthe low voltage secondary leads to the wired radio receiver in the homeof the subscriber. The feeders extending from the substation aregenerally polyphase, with the distribution transformers connectedbetween each of the phases. The usual transformers are of differentsizes, depending upon the load conditions, and may range from 0.5 to 50kva.; furthermore, in their distribution along the feeder no particularregularity in size is met; for example, a 5 kva. transformer may befollowed by a 25 kva. transformer, in turn followed by a 15 kva. unit,etc.

Referring to Fig. 1, there is shown a typical primary feeder A-A, B--B,supplying two transformers T1 and T2, to the low voltage secondaries ofwhich are connected the light load l, and single wired radio receiversrepresented in their entirety by the numeral 2. It will be noted thattransformers T1 and T2 may be separated by only a few, or by severalhundred or by several thousand feet, and that the low voltage secondarylines actually extend some distance from the transformer beforeconnected lights are met, all of such variations depending upon the lineconditions.

Referring now to Figs. 1 and 2, in the former the high frequencycurrents are traversing conductors, A-A, B-B, and will establish avoltage between points A-B. Now experiment has shown that viewed fromthe primary or high voltage winding, at the wired radio frequencies, atransformer will have a varying impedance which with increasingfrequency will increase, attain a maximum value, and then decrease. Themanner of variation is shown in Fig. 2, where T1, T2, T3, are impedancecurves for transformers T1, T2, T3. The maximum impedance occurs at thenatural frequency of the transformer. For example, a certain 10 kva.transformer had a natural frequency of 37.5 kilocycles at which theimpedance was in the neighorhood of 25,000 ohms, decreasing toapproximately 3000 ohms for lower and higher frequencies.

It is to be expected, therefore, that for frequencies in the proximityof the natural frequency the behavior of the transformer will beerratic. Since in wired radio broadcasting it is necessary to considerbands of frequencies instead of single frequencies, and as pointed outpreviously, the number, method of distribution, and size of thetransformers scattered along the feeder may vary greatly, it is obviousthat for certain frequencies greater transmitting powers will berequired than for others, or for the same transmitting power more energywill get through on some frequencies than on others, a feature whichleads to distortion of the received signal unless corrected.

Experiment has revealed, however, the important fact that substantiallyregardless of the type and size of the transformer under the normal loadconditions, the natural frequency will be somewhere in the range 25 to45 kilocycles, indicated by Af in Fig. 2. It is also the case, that thisparticular range of frequencies lies directly in the range which must beused for wired radio broadcasting. By my present invention I provide away of altering the natural frequency of distribution transformers so asto correct for their erratic behavior, which for a given set of feedersmay be done in a aduated manner, thereby obtaining a uniorm energyattenuation over the feeder for the entire band of frequencies usable inwired radio broadcasting.

Reference is made to Fig. 3 which is in general similar to Fig. 1, butin addition shows condensers 3 and 4 connected in parallel with theprimary windings of transformers T1 and T2, res ectively. I'Vithproperly chosen values o capacities condensers 3, 4, the naturalfrequencies of transformers may be made substantially the same andreduced to lie without the wired radio range. IVth this connection theinput impedances of the different transformers may be made to havemaximum values at substantially the same frequency without the wiredradio range, and to have substantially the same and uniformly varyingimpedance for all wired radio frequencies. This condition is representedin Fig. 4. A greatly improved transmission system from the highfrequency standpoint is thus obtained. From the low frequency powerstandpoint, the presence of condensers on the lines acts to compensatefor the lagging power factor normally existing, thereby increasing theefficiency of power transmission.

It is to be noted that condensers 3, 4, do not function as' by-passingunits but serve to alter the impedance of the transformer as a whole. Bythe arrangement of correcting circuits for various power transformers,carrier currents may be more efficiently distributed over a powernetwork of a city and the subscribers homes or lighting customers moreadequately supplied with the broadcast programs. By graduating theimpedance of the several transformers in the system the high frequencyenergy may be equalized throughout the system so that the volume of thereproduced signaling energy may be rendered more uniform to the varioussubscribers over a vast area.

While I have described my invention in one of its preferred embodiments,I desire that it be understood that modifications may be made but thatno limitations upon my invention are intended other than are imposed bythe scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. A wired radio system com rising a power transmission line arrange tohave high frequency carrier currents impressed thereon, powertransformers, each including primary and secondary windings, with theprimary windings thereof connected with said power transmission line,and means for modifying the characteristics of each of said primarywindings for offering substantially uniform impedances with respect tothe transmission of wired radio frequency currents. f

2. A wired radio system comprising a power transmission line arranged tohave igh frequency carrier currents impressed thereon, powertransformers, each including primary and secondary windings, with theprimary windings thereof connected with said power transmission line,and means oonnected in shunt with said rimary windings for altering thenatural requency of sald windings and effecting uniform distribution ofhigh frequency signaling ener in the secondary windings of said transormers.

3. A wired radio system comprising a ower transmission line arranged tohave igh frequency carrier currents impressed thereon, a plurality ofpower trans ormers each having primary and secondary windings, with theprimary windings thereof each having their impedances equalized for aselected band of signaling frequencies for obtaining a uniform energyattenuation over the transmission line for the entire band of wiredradio frequencies impressed thereon.

4. A wired radio system comprising a power transmission line arranged tohave high frequency carrier currents impressed thereon, a plurality ofpower transformers, each having primary and secondar windings, separatefeeders connected with said secondary windings, and condensers ofselected capacity values inde endently connected in shunt with saidprimary windings for equalizing the natural frequencies of saidtransformers and effectin uniform energy attenuation over said fee ersfor selected bands of frequencies.

5. A wired radio system comprising a nasales 3 power transmission linearranged to have high frequency carrier currents impressed thereon, aplurality of power transformers, each having primary and secondar wind-5 ings, separate feeders connected with said secondary windings, andcondensers of selected capacity values independently connected in shuntwith said primary windings for equalizing the natural frequencies ofsaid transformers and effecting uniform 10 energy attenuation over saidpower transmission line.

In testimony whereof I af'x my signature.

ROBERT D. DUNCAN, Jn.

